Metal 1,2 dithiolenes

ABSTRACT

A metal complex of the formula:   WHEREIN Me is selected from the group consisting of metals of the first, second, and third transition metal series which will provide a complex that is an effective infrared absorber and which is effectively transparent to light in the visible region of the spectrum; and each R is selected from the group consisting of alkyl, aromatic, heterocyclic and nuclearly substituted aromatic and heterocyclic rings, provided that at least two of said R moieties are different.

United States Patent 1 Bloom METAL 1,2 DITHIOLENES {75] Inventor:Stanley Morton Bloom, Waban.

Mass.

[73] Assignee: Polaroid Corporation, Cambridge,

Mass.

[22] Filed: May 8, 1972 [21] Appl. No.: 251,284

Related US. Application Data [62] Division of Ser. No. 60982, July 6,1970, Pat. No. 3,687,862, which is a division of Ser. No. 577,576, Sept.2, 1966. Pat. No. 3,588,216.

[52] US. Cl 260/429 11,117/333, 252/300, 260/3131, 260/329 ME, 260/3323R,

[51] Int. Cl. C07f 15/00, C07f 15/04 8] Field of Search 260/439 R, 429 R[56] References Cited UNITED STATES PATENTS 7/1966 Benson 260/42991/1968 King 260/429 R 8/1968 Mosby et a1. 260/4297 OTHER PUBLICATIONSSchrauzer et al., J. A. C. S. 87 (1965), p. 1483-9.

[ 51 Apr. 1, 1975 Schrauzer et al., Ang. Chem. Int. Ed. English, 3(I964). p. 381.

Primary ExaminerArthur P. Demers Attorney, Agent, or Firm-John P. Morley[57] ABSTRACT A metal complex of the formula:

5 Claims, 6 Drawing Figures METAL 1.2 DI'IHIOLENES CROSS REFERENCE TORELATED APPLICATIONS This application is a division of U. 5. PatentApplication Ser. No. 60,982 filed July 6, 1970 now US. Pat. No.3,687,862 which in turn is a division of Application Scr. No. 577,576filed Sept. 2, 1966 and now US. Pat. No. 3,588,216.

This invention relates to infrared (IR) absorption and, moreparticularly to novel products and procedures directed thereto.

A primary object of this invention, therefore, is to provide novelplastic products including means for absorbing in the infrared,particularly in the near infrared, and novel processes employing thesame.

Another object is to provide novel products and processes fordiminishing to an appreciable extent transmission of light both in thevisible and in the infrared regions of the spectrum.

A further object is to provide novel plastic optical elements includingan infrared absorber.

Still another object is to provide novel lightpolarizing elementsincluding means for absorption in the infrared.

Yet another object is to provide a novel sunglass structure having aplastic optical system including lightpolarizing means and means forabsorption in the infrared.

A still further object is to provide a class of compounds particularlyuseful for precluding transmission of infrared and novel processesemploying the same.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the processes involving severalsteps and the relation and order of one or more of such steps withrespect to each of the others, and the products possessing the features,properties and the relation of elements which are exemplified in thefollowing detailed disclosure, and the scope of the application of whichwill be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawing wherein:

FIG. 1 is an enlarged diagrammatic sectional view of a novel lens systemfor sunglasses or the like according to this invention;

FIG. 2 is a partially exploded, perspective view of novel sunglasses orthe like having the lens system of FIG. I;

HO. 3 is a view similar to FIG. 1 of another lens system of thisinvention;

curves showing the light transmittance of a plastic sunglass lens withand without the IR absorbers of this invention; and

FIGS. 5 and 6 are graphic presentations of the light transmittancecurves of the IR absorbers illustrative of the class of absorberscontemplated by this invention.

As was mentioned previously, one aspect of the present invention isdirected to compounds which are especially useful for inhibitingtransmission ofinfrared radiation, particularly in the near infrared,i.e., absorbing 5 inrared radiation, and to products and processes cm-FIG. 4 is a graphic presentation including superposed ploying thesecompounds.

The infrared absorbers contemplated for use in the present invention maybe defined as a metal complex of a bis-[cisd ,Z-bis-(alkyl, hydrogen,aryl or heterocyclic) ethylene-l,Z-dithiolate]. They may also be definedmore simply as cne dithiol metal complexes.

These infrared absorbers may be represented by the following formula:

(A) S s R /t-ie .1 R s s R wherein:

Me is a metal of the first, second or third transition metal series,i.e., those elements of Group VIII of the table of periodic arrangementof the elements, e.g., nickel, palladium, or platinum, which willprovide a complex which is an effective IR absorber and which issubstantially or effectively transparent to light in the visible regionof the spectrum, e.g., from about 4()0700p.;

each R, which may be the same or different, is hydrogen, alkyl, anaromatic or heterocyclic ring, or a substituted derivative thereof,e.g., alkoxyalkyl, alkyl and/or alkoxy-substituted aromatic and heterocyclic rings, substituents of the foregoing description containingelectron withdrawing groups, etc.

As examples of useful alkyl radicals contemplated by said R moieties,mention may be made of lower alkyl radicals containing l-6 carbon atoms,e.g., methyl, ethyl, propyl, isopropyl, butyl, etc. As examples ofuseful aromatic rings, including substituted derivatives thereof,mention may be made of phenyl, naphthyl, methyl-phenyl, methylnaphthyl,alkoxyphenyl and alkoxynaphthyl, e.g., dodecyloxyphenyl,halosubstituted, particularly fluoro-substituted, -alkylsubstituted,amino, including dialkylamino -substituted, haloalkyl-substituted, e.g.,trifluoromethylsubstituted phenyl and naphthyl radicals, etc.

As examples of useful heterocyclic rings, mention may be made of thoseof the formula:

where X is nitrogen, oxygen, or sulfur, and substituted derivativesthereof, including benz-substituted derivatives.

The following compounds are illustrative of useful IR absorbers withinthe scope of Formula (A):

The compounds of Formula A are in general previously known in the art,although certain of the disclosed species, particularly the asymmetricalspecies, e.g., those of Formulae 3, 8,9, l(), 13, l4, l6, l7, l8,

and I9 are believed to be specifically novel. (See for 3Q of Formula Amay accordingly in general be prepared 35 in the manner heretoforedescribed in the literature.

For example, they may be prepared by reacting p 8 with a compound of theformula:

wherein R has the meaning heretofore noted, to form a compound of theformula:

which is then reacted with a suitable inorganic salt containing thedesired metal, Me, e.g., NiCl2 61-120, PtCl PdCl2, K PtCh, K PdCl etc.,to prepare the desired compound of Formula A. Symmetrical compounds,i.e., where each R is the same, are obtained by using a single compoundof Formula B wherein each R is the same. Asymmetrical compounds (such asthose of Formulae 8 and 9) may be obtained by employing two differentcompounds of Formula B as starting materials. In like manner, one or twocompounds of Formula B in which each R is different, may be exployed toprovide compounds of Formula A wherein two or more of the R moieties aredifferent.

The compounds of Formula (A) have been found to possess exceptionallydesirable spectral absorption characteristics. As a class, they havebeen found to be relatively narrow band" absorbers which have a A in thenear infrared region of the spectrum, substantially no absorption in thevisible region, i.e., are substantially transparent to visible light,and a A in the ultraviolet region of the spectrum, primarily in the farultraviolet region. They are thus particularly useful in optical systemswherein it is desired to transmit visible light while absorbing light inthe designated invisible regions of the spectrum, that is, to reduce orminimize transmission in the near infrared and/or in the ultravioletregion of the spectrum. The spectral absorption characteristics of thesecompounds may be more readily understood by reference to FIGS. 5 and 6wherein spectral absorption curves of two compounds illustrative of theclass, specifically, those of Formulae 5 (shown in dotted line) and 6(shown in solid line) are superposed. It will be observed that the A andUV of the compounds are shifted by substitution of the eomplexing metal.They may also be shifted by changing the substituents of the R moiety,so that by so doing it is possible to provide narrow band filters forvarious portions of the IR and UV regions of the spectrum.

In addition to their exceptional spectral absorption characteristics,the compounds have been found to be extremely stable to the degradativeforces of light, heat,

and humidity. Since IR absorbers as a class are quite unstable to suchconditions, this stability of those compounds of Formula A is quitesurprising.

A representative class of these compounds was tested for stability tolight, heat, and humidity by imbibing onto each of three sheets ofcellulose acetate butyrate a solution consisting of the compound to betested dissolved in a suitable organic solvent. Each of the imbibedsheets was then subjected to one of the following standard testprocedures: (I) light stability under a xenon arc lamp; (2) relativehumidity (moisture plus heat); and (3) dry heat. Stability was tested bydetermining the density before and after each test. The following chartshows the results ofthese tests, the figures given representing thepercent of fading (loss of den sity) after the recited time interval.

thus minimize transmission of radiation which may be harmful to the eye.

An important aspect of this invention, therefore, is the conceptofemploying an infrared absorber in plas- TABLE I Compound Solvent XenonAre Relative Humidity Dry Heat (Formula No.) tU.V Shieltll (95% at lllFlll5llFI l tetrahydrot'uran 2.4M IIZI) hrs) (LOW; (251) hrs) 8.2'71' I250hrs) 2 CHCI, (LIV/l [120 hrs) 2.0); (l2ll hrs) [LIV/1' 1 I hrs) 4 CHCl,2)? (I70 hrs) 3' H70 hrs) 5% (170 hrs) 7 tetrahydrot'urnn 3.5)? [120hrs) 2.30? (250 hrs) 3.5); (250 hrs) 8 CHCL, 2.6% H75 hrs) l,7'/r (I75hrs) L3); H75 hrs) l2 CHCI 3.0); H70 hrs) 1.4% (170 hrs) 0.0% H70 hrs)As was mentioned previously, the aforementioned infrared absorbers areparticularly useful in plastic optical products which, unlike glassoptical products, do not possess a molecular structure that willinherently absorb in the infrared region. Of particular interest in thepractice of this invention are plastic sunglasses such as those known inthe art as polarizing sunglasses.

A typical plastic sunglass of this nature has an optical systemcomprising a light polarizer laminated between two sheets of transparentplastic, the outer or free surfaces of which may be provided with anabrasiveresistant coating. The polarizing sheet may for example be amolecularly oriented plastic sheet material which has been stained ordyed to render it light polarizing, e.g., molecularly oriented polyvinylalcohol stained with iodine; the transparent plastic between which thepolarizing sheet is laminated may, for example, be a thermoplasticcellulose derivative, e.g., cellulose nitrate, cellulose triacetate,cellulose acetate propionate, cellulose acetate butyrate, ethylcellulose, etc.', and the abrasive-resistant coating may, for example,be a complctely polymerized melamineformaldehydc resin, a thermosetting,cross-linked polymer such as a diethylenic-substitutedpolyalkyleneglycol, e.g., polymeric coatings formed by in situpolymerization of polyalkyleneglycol diesters of a-B-unsaturatedcarboxylic acids on the plastic sheet material, etc. Plastic laminationsincluding materials of this description are disclosed for example, inUS. Pat. Nos. 2,237.567; 2,527,400; 2,554,850; 3,08l,l92; and 3,097,106.

While polarizing sunglasses of the foregoing description effectivelydiminish transmission of visible light to a desired comfortable level,e.g., to say from about 20-30% of the visible solar energy, anappreciable amount of invisible radiation, primarily in the ultravioletand near infrared regions of the spectrum, is transmitted. By way ofillustration, the solar energy at the lens of the eye is shown by one ofthe superposed curves on FIG. 4. From this curve it will be seen thatappreciable solar energy both in the near infrared and e in theultraviolet regions of the spectrum is present at the lens. Theultraviolet is substantially absorbed at the lens, but the IR passesthrough.

In view of the foregoing discussion, it is quite surprising that whileit has heretofore been suggested to cmploy ultraviolet absorbers in suchoptical products to protect the lens, it is believed and understood thatno one has heretofore employed an IR absorber in such plastic opticalproducts. The failure to do so is believed to be at least in part due tothe inherent instability to light of IR absorbers as a class and may inpart be due to the failure to appreciate the advantages of employ ingsuch IR absorbers. Infrared absorbers which also have good ultravioletabsorption, as herein disclosed,

tic optical products such as sunglasses of the foregoing generaldescription.

This aspect of the invention will be more readily understood byreference to FIGS. 1-3 of the accompanying drawings.

As shown in FIG. I, one embodiment of this aspect of the inventioncomprises a plastic optical element I, the outer surfaces of which areprovided with an abrasive-resistant coating 16, such as those heretoforedescribed. Betwecn these outer layers are positioned, as by lamination,a pair of substantially or effectively transparent sheets of plastic 12,c.g., cellulose acetate butyrate, cellulose nitrate, cellulose acetatepropionate, cellulose acetate, ethyl cellulose, etc; a pair of layers orcoatings 14 containing an IR absorber, e.g., one or more of the IRabsorbers of Formula A, and a polarizing sheet material 10, e.g., amolecularly oriented polyvinyl alcohol sheet which has been stained withiodine to render it light-polarizing and which may also have beenborated in the manner disclosed in any of US. Pat. Nosv 2,445,579, Re:23,297 or 2,554,850.

The thicknesses of the various layers in the aforementioned plasticoptical elements are not critical and may vary over wide ranges. It willbe appreciated, however, that the layers are preferably as thin aspossible, for reasons of economy, weight and to minimize distortion orrefraction of transmitted light. By way of example only, theabrasion-resistant coating layers each may be on the order of 1 milthick; the transparent plastic sheets may each be on the order of0.0l20-00 l 40 inch thick; the polarizcr on the order of 0.00l inch thick;and the IR absorber-containing layers each on the order of about 0.1 toabout 5.0 mil thick.

The IR absorber-containing layers may be applied as a coating comprisinga viscous solution containing the same or they may be imbibed into thetransparent plastic sheets by contacting them with a solution containingone or more of the absorbers. The former method of application ispreferred, however, since it has been found that greater amounts of theabsorber can be added a coating than can be added by imbibition. It willbe appreciated, however, that even when applied as a coating, some ofthe absorber may inherently be imbibed. Whether the IR absorber is addedas a coating or by imbibition, useful solvents for that purpose includechloroform, methylene dichloride, toluene, tetrahydrofuran, etc., andmixtures of such solvents.

In addition to the layers or coatings shown in FIG. 1, the element maycontain other layers introduced to provide suitable bonding surfaces toinsure obtaining a strong lamination.

It will be appreciated that the plastic element is not restricted to therelationship of layers shown in FIG. I. For example, the IR absorber maybe present between the outer coating 16 and the transparent plasticsheet 12. (In the event a scratch resistant coating 16 is applied by insitu polymerization, care should be exercised to avoid the use ofpolymerization catalysts, e.g., peroxides, which might attack theinfrared absorber.) In lieu of having two separate layers 14 of lRabsorber, a single such layer may be provided, as shown in FIG. 3. Inany event, optical elements of this invention may be employed inconventional eyeglass frames 18, as shown in FIG. 2.

As was mentioned earlier and illustrated in the spec tral absorptioncurves shown in FIGS. -6, while the compounds of Formula A are extremelygood absorbers in the near infrared region of the spectrum and aresubstantially transparent to visible light, they also absorb appreciablyin the ultraviolet region. This latter property makes it possible toeliminate or to materially reduce the amount of ultraviolet absorberneeded in such an element to protect the lens of the eye. Thus, thesecompounds may be said to serve a dual function in reducing thetransmission of harmful invisible radiation at both ends of thespectrum.

The amount of the IR absorber employed in the plastic optical elementsof this invention may vary over a wide range, the amount employed beingin part dependent upon the percent of transmission in the region desiredand is in part dependent upon the efficiency of the absorber in thesystem employed. In a preferred embodiment, however, the IR absorber ispresent in an amount such that the amount of transmitted IR is notsubstantially greater, if greater at all, than the amount of visiblelight transmitted. By not substantially greater," it is meant that thepercent of IR transmitted does not exceed the percent of visible lighttransmitted by more than about 5 percent.

Since the compounds of Formula A are relatively narrow band absorbers,it may be desirable to employ a mixture of two or more such compounds ofvarying A to provide effective absorption over the necessary range ofthe infrared region of the spectrum.

While the foregoing description of plastic optical elements has, forpurposes of illustration, been in terms of polarizing sunglasses, itwill be appreciated that the invention is not limited thereto. Since animportant aspect of this invention is the discovery that compounds ofFormula A effectively diminish transmission of substantial amounts ofunwanted invisible radiation while being substantially transparent tovisible light and possessing extremely desirable stability to light,heat and humidity, this invention also contemplates the use of thecompounds of Formula A in various systems wherein it is desired totransmit visible light but to diminish or retard transmission ofinvisible radiation in particular regions of the spectrum. Since thesecompounds possess narrow absorption bands they may be employed singly toprovide absorption in a particular narrow band of the spectrum or incombination to provide broader absorption. The ability of the individualcompounds to provide narrow absorption in a desired region is asignificant advantage which will be apparent to those skilled in theart. Accordingly, the various other systems to which this invention isapplicable, eg, in plastic lenses for use in photography, will bereadily suggested to those skilled in the art in the light of thisdescription.

The following examples show by way of illustration and not by way oflimitation the preparation of the novel compounds of this invention, theA of each of the compounds being determined in dichloromethane.

EXAMPLE I The IR absorber of Formula 1 was prepared by refluxing l moleof:

OCH

EXAMPLE 2 Substitution of benzoin for the acyloin of Example I yieldedthe compound of Formula 2, m.p. 282-283C nuu' IL;

EXAMPLE 3 Substitution of:

Th3 C O H C: OH CH in the procedure of Example I yielded the compound ofFormula 7, m.p. 255-256C; a 773 u; e l9,600.

EXAMPLE 4 Repetition of Example I, employing a large excess of benzointo avoid loss of the metal, and employing Kz tCh yielded the compound ofFormula 6, m.p. 310; A 800 a; e 5 l ,600.

EXAMPLE 5 Substitution of the acyloin in the procedure of Example 4yielded the compound of Formula l2, m.p. 3033()5C; k 863 pt; 41,600.

EXAMPLE 6 Substitution of:

in the procedure of Example 4 yielded the compound of Formula I l m.p.350C; )t,,,,, 740 a; e 36,800. EXAMPLE 7 Substitution of K2PdCl4 in theprocedure of Example 4 yielded the compound of Formula 5, mp. 254C; A=885 ,u; 5 37.900. EXAMPLE 8 Substitution of K PdCl in the procedure ofExample 5 yielded the compound of Formula 4, mp. 250C; A 948 u; e I37.900.

EXAMPLE 9 4.4'-diisopropyl benzoin was prepared according to thesynthesis described in Ben. 77. 409 (1944). This compound wassubstituted for the acyloin in the procedure of Example l to yield thecompound of Formula l3. m.p. 305307C; A 828 u; E 49,200.

EXAMPLE l0 p-butoxybenzaldehyde was made by the method described inStoermcr, Ber. 61,2328 (I928). This was in turn used to make4.4-dibutoxyben7.oin in the manner described in Tadros. J.(7mm.Soc.,(l9f13),4527. Substitution of this bcnzoin for the acyloin ofExample I yielded the compound of Formula l4. m.p. 239-240C1 A 930; e35.600v

EXAMPLE ll Substitution of a-bromoacetophenone for the acyloin ofExample 1 yielded the compound of Formula as an impure mixture which wasnot purified. HBr gas was evolved during the reaction. Analysis of theimpure Cpd', )t,,,,, 8l5 1.1.; e I 7000.

EXAMPLE l2 The thenoin:

was synthesized according to the procedure described in J. Org. Chem.l4. 184 (1949). g. of this compound (0.088 mole) and 57.5 g. of P 8(0.13 mole) were refluxed with stirring for six hours in 300 ml. ofdioxanc. The reaction mixture was cooled and a black residue wasfiltered off. To the filtered solution was then added 20.8 g. of NiCl.6H O (0.088 mole) dissolved in 100 ml. of H 0. The mixture was heatedon a steam bath for one hour to form black crystals which were collectedby cooling and filtering to yield l.l g. of the compound of Formula 3.This compound was purified by dissolving the crude product in 600 ml. ofCHCl filtering and evaporating the CHClg down to about ml. and allowingthe product to crystallize out. mp. IMP-251C; )t,,,,, 970 u; e 24,6000.

EXAMPLE 13 The procedure of Example 1 was repeated using as startingmaterials a 3:l ratio of benzoin to anisoin to yield the compound ofFormula 8, mp. 26l263C;

EXAMPLE l4 Substitution of K PdCl in the procedure of Example 13 yieldedthe compound of Formula 10, mp 288290C, ma.z- 838 a; 6 42.000.

The following example shows by way of illustration and not by way oflimitation the preparation of an optical element in accordance with thisinvention.

EXAMPLE 15 To Hit) cc of chloroform was added 7.5 g of cellulose acetatebutyrate chips. To the resulting viscous solution was added a secondsolution containing 0.1 g. of the 1R absorber of Formula l, 0.1 g. ofthe IR absorber of Formula 7, and 0.02 g. of Calco Oil Violet ZlRS(tradename of American Cyanamid Company of a vio- 0 let dye which wasemployed to provide a neutral gray product) in 20 cc. ofchloroform. Theresulting mixture was coated onto each of two sheets of clear celluloseacetate butyrate at a speed ofo ft/minute to provide on each sheet alayer containing 0.020 g. of combined lR absorbers per sq. ft. ofsurface area, the layer or coating being approximately 0.3 mil thick. Onthe free surface of each sheet of cellulose acetate butyrate (thesurface opposite from that containing the IR absorber coating) there wasthen applied an abrasive-resistant coating such as described in ExampleI of the aforementioned US. Pat. No. 3.097,l06 containing 0.6perccnt byweight ol Uvinul 490'" (tradcname ofGcneral Aniline Company for anultraviolet light absorber]. The cellulose acetate butyrate on thesurface of each of the IR absorbenccllulose acetate butyrate coating wasconverted back to cellulose by treating it with a l:l:l solution ofsodium hydroxide, methanol and distilled water for l6 seconds at 46C.The converted surface of each sheet was then washed and the two sheetswere heated in an oven to drive off excess moisture. A solutioncontaining l.5 g. of polyvinyl alcohol (PVA) in 66.7 cc of water and33.3 cc of methanol was coated on each of the converted surfaces at 6ft/minute to provide a suitable bonding surface for the polarizer to belaminated therebetween. A molecularly oriented PVA (stretched four timesits original length) was laminated to the PVA coating on one of thesheets at room temperature by applying to the respective laminatingsurfaces a laminating dope comprising a 2'71 PVA solution in water andpressing the surfaces together. The molecularly oriented PVA was thenstained by imbibition in an iodine solution to render itlight-polarizing. It was then imbibed in a boric acid solution of lowconcentration, dried in vacuo to remove excess liquid, and baked in aheating chamber to dry. The other sheet was then laminated in a similarmanner to the free outer surface of the polarizer to provide a plasticoptical product containing two of the IR absorbers.

The plastic sunglasses prepared in Example 15 were compared with asimilar pair prepared in substantially the same manner but containing nolR absorbers. The latter sunglasses also contained a substantiallygreater amount of ultraviolet absorber than that which was added to theabrasive-resistant coating in the example. For comparison purposes. therespective sunglasses were identical in all other relevant components.The

transmission curves of the respective sunglasses are shown in FlG. 4superposed with the previously mentioned curve showing the solar energyat the lens of the 60 eye.

Looking first at the ultraviolet region (left sides of the graph), itwill be noted that the sunglasses without the lR absorber greatlydiminish the ultraviolet at the lens, transmitting 4% of the totalultraviolet while the sunglasses with the IR absorber nearly precludedany ultraviolet transmission, transmitting only 0.6% of the totalultraviolet thereby indicating the superiority of the sunglasses of thisinvention in the ultraviolet region.

With reference next to the visible region of the spectrum, thesunglasses without the lR absorber transmitted 24% of the Kv (energytransmitted at middle visual range, i.e.. about 550 a); whereas thesunglasses containing the lR absorber transmitted only slightly less.23%. thus indicating that there is no significant difference intransparency to visible light as a result of the incorporation of theinfrared absorbers of this invention.

In the near lR region (right hand side the sunglasses without the IRabsorber transmitted 59.5% of the total near infrared energy otherwiseavailable at the lens of the eye: whereas the sunglasses with theabsorber transmitted only 2871 of the total radiation in this region. itwill thus be seen that the latter sunglasses transmit no substantiallygreater per cent of the IR than they do visible light. It will beappreciated, moreover. that by employing one or more additional IRabsorbers having a A more towards the far infrared. the transmitted nearinfrared shown on the chart may be further reduced to levels as low orlower than the transmitted visible light.

As was mentioned previously, the asymmetrical compounds of Formula A arespecifically novel. These compounds provide the significant advantage ofmaking it possible to provide a particular compound having absorptionproperties over a particular desired narrow hand of the infrared region.By way of illustration, it will be noted from the illustrative examplesthat the symmetrical compounds of Formulae l and 2 have )t,,,,,respectively of 920 a and 865 14. Assuming it is desired to obtain acompound having 21 Am,- intermediate these two points in the spectrum,one may prepare the compound of Formula 8, which it will be noted has 21A of 895 ;1..

ln Example [5 illustrating the preparation ot a plastic optical elementin accordance with this invention. ref erence has been made to the stepof converting the cellulose acetate butyrate on the surface of the lRabsorber-cellulose acetate butyrate coating back to cellulose. Thisconcept is desecribed and claimed in the eopending application of HaroldO. Buzzell, Ser. No. 577.578 filed Sept. 2. I966 and now U.S. Pat. No.3,620,888.

Since certain changes may be made in the above product and processeswithout departing from the scope of the invention herein involved. it isintended that all matter contained in the above description or shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is: l. A compound of the following formula:

2. A compound of the following formula:

3. A compound of the following formula:

4. A compound of the following formula:

S. A compound of the following formula:

' S 0 CHCHCHCHO acacaea ll N ll en CH ca cno C 0

1. A COMPOUND OF THE FOLLOWING FORMULA:(PHENYL-C(-S(-))=C(-S(-))-)BENZENE . NI(+2) .1-((4-(CH3-O-)PHENYL)-C(-S(-))=C(-S(-))-),4-(CH3-O-)BENZENE
 2. Acompound of the following formula:
 3. A compound of the followingformula:
 4. A compound of the following formula:
 5. A compound of thefollowing formula: